As a fuel tank structure, there is a structure (a so-called airtight tank) in which a sealing valve is provided between a fuel tank and a canister, and the fuel tank is sealed at times other than at times of refueling the fuel tank or times when the tank internal pressure exceeds a predetermined value (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2011-226308).
In such a fuel tank structure, when the sealing valve between the fuel tank and the canister is opened in a state in which the tank internal pressure within the fuel tank is high, the high tank internal pressure acts on a valve that regulates the full-tank state of the fuel tank (a full-tank regulating valve), and there is the concern that the full-tank regulating valve will close. When the full-tank regulating valve closes, vapor within the fuel tank cannot be moved toward the canister side, and therefore, refueling and releasing of pressure can no longer be carried out.